Today I just discovered a small little disclosure issue with facebook and google. Actually, the discovery was due to my girlfriend.
When you enter a public facebook profile for a person, it will display five friends of that person. Since everybody who is friends with this person also have a public profile, which also lists five friends, there is a reasonable chance that the person turns up in their profile.
Google indexes these pages, so it is possible to search these public profiles. By searching for the a particular name on facebook using google, it is possible to find a lot more friends of the person. For instance, the query
will list a few of my facebook friends.
I imagine that it is possible to extract quite a big portion of the facebook social network using this method.